Global Space Charge Effect in SCALPEL

Coulomb interaction effects, such as stochastic trajectory displacements and global space charge, may limit the performance of charged particle projection lithography systems. While stochastic Coulomb interactions cause an uncorrectable image blur (that couples resolution and throughput), deterministic global space charge effects can be corrected or compensated in most cases. For instance, it is well known that if the current density distribution is uniform in every cross section of the beam in a probe forming system, global space charge will cause only image defocus and magnification change. In this case, the beam acts like an ideal negative lens; hence, its action can be simply compensated by a proper lens adjustment. If the current density is nonuniform, global space charge may also cause aberrations that can not be corrected by simply changing lens characteristics. The commonly accepted space charge lens concept has been previously used for the identification and evaluation of aberrations caused by space charge.